A Merged LNA-Mixer with Wide Variable Conversion Gain and Low Noise Figure for WLAN Direct-Conversion Receivers

kground and Objectives: In wireless communications, receivers play an essential role. Among receiver architectures, the direct-conversion receiver (DCR) architecture has been selected due to its high level of integration and low cost. However, it suffers from DC offset due to self-mixing, I/Q imbalance, and flicker noise.Methods: This paper presents a new LNA-mixer with variable conversion gain (VG-LM) for wireless local area network (WLAN) applications. A low noise transconductance amplifier (LNTA) is used as the transconductance stage in the Gilbert cell mixer. The wide variable conversion gain range is achieved by the change in LNTA’s transconductance and transconductance of the mixer switching transistors.Results: The proposed LNA-mixer is designed and simulated using ۰.۱۸µm CMOS technology in Cadence Spectre RF. The post-layout simulations exhibit the proposed circuit operates at ۲.۴ GHz with a bandwidth of ۱۰ MHz. In addition, the conversion gain is changed from -۳.۹ dB to ۲۳.۹ dB with the variation of the controlled DC voltage from ۰.۵ to ۱.۸. At the high gain, the double-sideband noise figure (DSB-NF) is less than ۳.۷ dB, and its third-order intermodulation point (IIP۳) is -۹ dBm. The power consumption is ۲۲ mW from the supply voltage of ۱.۸ V. The circuit occupies ۷۴۳ µm×۷۷۵ µm of core chip area.Conclusion: Using the proposed circuit, the RF front end receiver does not need the low noise amplifier (LNA) and variable gain amplifier (VGA).

Keywords:

Variable Conversion Gain , Low Noise Transconductance Amplifier (LNTA) , Active mixer , Noise figure